KANDAHAR AIR FIELD, Afghanistan -- Sometimes they come in ones and twos. Sometimes, they arrive in convoys of dozens, all of them caked in layers of dirt, bugs, spent shell casings and other grime gathered over months of driving and fighting in Afghanistan.

Now, on their way back to the United States as the military reduces its presence, dirty vehicles and other equipment pose a challenge not faced when they were shipped into Afghanistan.

Like tourists returning from vacation, the military has to abide by U.S. Department of Agriculture and Department of Defense regulations designed to keep dirt and agricultural hazards such as spiders and insects out of the United States, and dangerous items out of international ports.

Less than a year ago, it took about 100 days to clean, inspect and prepare an armored vehicle for the move home. Now, with a greater focus on the drawdown and boosted by more than 300 contractors, the 4th Battalion, 401st Army Field Support Brigade at Kandahar Air Field can process a vehicle in a week.

“It’s become a priority for everyone now,” said Army Capt. Lee Berry, who helps oversee the battalion’s Redistribution Property Accountability Team yard at Kandahar, where military units departing from across southern and western Afghanistan drop off vehicles and other equipment. Other elements of the 401st Army Field Support Brigade operate a similar facility at Bagram Air Field for equipment from units in the north and the east.

In addition to being weighed and measured, stripped of extra equipment such as radios and turrets and being tagged with bar codes for tracking, vehicles that arrive at Kandahar go through at least five inspections by Berry’s teams and by the units dropping them off, as well as four searches by members of the military who have been deputized to conduct customs and agricultural inspections.

“The military deals with the same customs standards as civilians,” said Petty Officer 1st Class Joseph Toth, a Navy torpedoman’s mate and one of the customs inspectors at the site.

The inspectors look for everything from spent or live ammunition and explosives, to “pinchable” amounts of dirt that could hide invasive species of insects or other organisms, he said. Soldiers also report coming across items such as birds’ nests, dead animals, or forgotten smartphones or music players.

In between the inspections, each vehicle is cleaned using pressure washers on massive concrete wash racks. According to Berry, a complete washing that meets custom standards can take anywhere from six hours for the average armored vehicle, to 36 hours for the more complicated Stryker vehicles.

Currently the yard at Kandahar can handle 24 vehicles at a time, but the operation is scheduled to soon move to an indoor facility that will be able to process 52 vehicles at a time. Keeping the process indoors will also cut down on dirt and bugs that collect while the vehicles sit outside.

The battalion also plans to install 10 wash racks for smaller equipment, which will free up the large racks for more vehicles. A vehicle wash rack is also being installed next to the airfield itself, which will allow vehicles to be washed down one last time before being loaded on aircraft.

Despite all the additional resources, however, challenges remain.

Amid the drawdown, combat units are often in the difficult position of fighting as they withdraw, complicating efforts to collect their equipment.

“It’s not that they don’t care, it’s just that they have a different mission than us,” Berry said, noting that teams of contractors have been assigned to help units prepare to turn in their equipment.

Another challenge that Berry says can become a bottleneck is a lack of options when it comes to shipping the equipment out of Afghanistan.

Unlike Iraq, where convoys of vehicles could be driven to ports in neighboring Kuwait, landlocked Afghanistan’s has forced NATO officials to negotiate exit routes through Pakistan. Pakistan and the United States signed an agreement re-opening some supply routes into Afghanistan in July 2012, but details on shipping coalition war materiel out of Afghanistan are still being worked out.

That’s a cause of uncertainty for military units tasked with shipping the massive amounts of equipment that are processed and cleaned at places like Kandahar.

The Air Force units at Kandahar flew out an all-time high 129 MRAP armored vehicles in December, a significant increase over the previous high of 25 in a month, said Air Force Lt. Col. Manuel Perez, 451st Expeditionary Logistics Readiness Squadron commander. But even that is a drop in the bucket compared to the 300 to 400 vehicles that Berry says come through his yard each month. About 60 percent of those vehicles are being flown out by contract carriers.

Piedade Cardozo, a contractor for AC First, washes down a U.S. military armored vehicle at Kandahar Airfield, Afghanistan, before the vehicle is shipped back to the States. All military equipment must meet Agriculture Department and customs regulations designed to keep such things as foreign insects out of the United States.Josh Smith/Stars and Stripes